1. Field of the Invention
The present invention relates to a camshaft for actuating valve tappets in internal combustion engines. The camshaft includes a shaft member and at least one cam member slid onto and connected to the shaft member. For sliding the cam member onto the shaft member, the cam member defines an axial bore having a shape which essentially corresponds to the cross-sectional profile of the shaft member.
2. Description of the Prior Art
Camshafts of internal combustion engines are highly stressed structural machine parts. The large number of prior art publications in this area make it clear that substantial efforts have been made to find economical and technically satisfactory solutions for manufacturing useful camshafts.
It is to be particularly emphasized that during operation a camshaft is subjected to extreme dynamic stresses as a result of the type of task it has to perform. Thus, in all camshafts which have become known in the past, the connection between cam member and shaft member is an integrally formed metal connection and/or a positively locked connection. Substantial searches performed in the relevant field in the patent literature have not developed any other structural solutions than the already mentioned connection between cam member and shaft member which is an integrally formed metal connection and/or a positively locked connection.
In particular, camshafts are known in which the cams and the shaft are manufactured separately and are subsequently joined together to form a structural unit. In a known construction of this type, German Offenlegungsschrift No. 28 38 995 and German Offenlegungsschrift No. 33 21 846, the shaft is provided with a plurality of axially extending grooves and the bore in the cam has a corresponding radial projection which engages into one of these grooves. The bore of the cam surrounds the shaft with play and the aforementioned projection has such a size in radial direction that cam and shaft can be joined together and are locked together by means of a frictional engagement. The gap resulting from the aforementioned play is being filled with brazing solder from the outside after cam and shaft have been joined together. The number of grooves provided circumferentially on the shaft corresponds to the cam phase relationship required for the respective purpose of the camshaft. This construction is not advantageous because it is very difficult to manufacture the grooves on the shaft in exactly the correct position. These grooves must be manufactured very precisely, i.e., they must be exactly positioned with respect to their angular location.
U.S. Pat. No. 3,543,589 shows and describes a cam disk with balanced, spring-loaded feeler rollers. The cam disk has a plurality of essentially equal cam pumps which are uniformly distributed around an axis. In addition, two spaced-apart distance rollers are provided in such a manner relative to the cam disk that, when one feeler roller is on an ascending portion of a cam hump and, thus, removes energy from the drive mechanism, the other feeler roller rolls on a descending portion of a cam hump and, thus, returns energy into the system, wherein the energy returned is the same as that being removed from the system by the first feeler roller. The drawings of this patent illustrate this concept. The drawings also show the construction of the cam disk or control switch. A cam disk having an even number or an odd number of cam humps is arranged on a shaft of circular cross-section. The shaft is not indicated in detail. The feeler rollers are supported by resilient plates which, in turn, have electrical contacts, the feeler rollers are located relative to the cam disk in such a way that, when the cam disk is rotating, one of the feeler rollers rolls upwardly on a cam hump, while the other feeler roller simultaneously rolls down such a cam hump. The connection between the drive shaft and cam disk is formed by a hollow cylindrical element which is made of a macromolecular material. This prior U.S. patent does not show or describe a camshaft for internal combustion engines; rather, it describes a control shaft with a cam disk for actuating electrical plate contacts. The cam disk for controlling the feeler rollers or the switching springs can only handle small loads. The cam disk is to be uniformly stressed during a full rotation. The principal concept on which the prior aforedescribed construction is based is the energy recuperation and the resulting reduction of the torque of the drive motor.
It is also known in the art to use a so-called tolerance ring for a frictionally locking engagement between a shaft and a hub. This tolerance ring is an undulated spring steel strip which is bent into an open ring having a longitudinal slot. This ring is either slid onto the shaft or inserted into the hub bore. The size of the ring is such that, when the ring is inserted, the edges defining the longitudinal slot are spaced apart from each other. Once the parts to be joined have been put together, the tolerance ring, due to the aforementioned longitudinal slot, can slightly yield in radial direction as well as in circumferential direction in dependence upon the forces and moments acting on the machine elements connected by the ring. These so-called tolerance rings have been found very useful in general mechanical engineering because they facilitate a quick, inexpensive assembly and a simple construction of parts to be connected. The rings can compensate to a high degree different thermal expansions between machine elements of the different materials. The rings are resistant to temperature changes, they permit great tolerances between parts to be connected and, moreover, they are resistant to chemical attack.
A camshaft is a machine element of a special type, especially because during normal operation, it is subjected to very extreme dynamic loads. Thus, in the past, all cam shafts have a connection between shaft and cam which is an integrally formed material connection and/or a positively locked connection.
It is, therefore, the primary object of the present invention to simplify the manufacture of such a camshaft and, simultaneously, to improve its quality, while the shaft and the cams are still connected to each other only by frictional engagement and structural elements are used which are known for such a connection.